A multi-vehicle accident on the southbound lanes of the NJ Turnpike killed three people from Georgia and left parts of the roadway shuttered for hours, leading to heavy backups and congestion.

Lt. Stephen Jones says police are still investigating what caused a tractor-trailer to hit the back of a Toyota Camry around 10 AM Thursday below Exit 5 near Mount Laurel.

Three people and a dog in a silver Toyota Camry died, and the occupants are believed to all be from Stone Mountain Georgia. Jones says the Camry’s 51-year-old male driver, a 49-year-old female and a 12-year-old male were all pronounced dead at the scene. An 18-year-old woman from the same car was treated for minor injuries at Cooper Hospital.

Jones says a second car was involved in a minor way, and a second tractor-trailer swerved to avoid the accident. The occupants of both tractor trailer trucks were uninjured, and another driver of a Ford Edge was also unharmed.

All southbound lanes of the NJ Turnpike have been re-opened following the crash.

(The Associated Press contributed to this report)